To meet the recent demand for higher integration in integrated circuits, a finer feature size is required for pattern formation. In forming resist patterns with a feature size of 0.2 μm or less, chemically amplified resist compositions utilizing photo-generated acid as the catalyst are typically used in the art because of high sensitivity and resolution. Often, high-energy radiation such as UV, deep UV, EUV or electron beam (EB) is used as the light source for exposure of these resist compositions. Among others, the EB or EUV lithography is recognized most attractive because ultra-fine patterns are expectable.
Resist compositions include positive ones in which exposed areas are dissolved away and negative ones in which exposed areas are left as a pattern. A suitable composition is selected among them depending on the desired resist pattern. In general, the chemically amplified negative resist composition comprises a polymer which is normally soluble in an aqueous alkaline developer, an acid generator which is decomposed to generate an acid upon exposure to light, and a crosslinker which causes the polymer to crosslink between molecules in the presence of the acid serving as a catalyst, thus rendering the polymer insoluble in the developer. Typically a basic compound is added for controlling the diffusion of the acid generated upon light exposure.
A number of negative resist compositions of the type comprising a polymer which is soluble in an aqueous alkaline developer and includes phenolic units as the alkali-soluble units were developed, especially for the KrF excimer laser lithography. These compositions have not been used in the ArF excimer laser lithography because the phenolic units are not transmissive to exposure light having a wavelength of 150 to 220 nm. Recently, these compositions are recognized attractive again as the negative resist composition for the EB and EUV lithography capable of forming ultra-fine patterns. Exemplary compositions are described in JP-A 2006-201532, JP-A 2006-215180, and JP-A 2008-249762.